It is frequently necessary in surgical operations in the craniofacial region to reposition and then to fix, after the end of the surgical operation, a fragment of the skull sawn-out from the skull bone or alternatively, to substitute areas of the bone removed during the operation with a plate consisting of a suitable biocompatible material, such as for example titanium. As in the craniofacial region no large forces act on the corresponding fixing points, the rigidity and in particular the pull-out resistance of the fixing plays only a subordinate role in this anatomical region. To fasten the sawn-out fragment of the skull or the plate in the desired position, self-drilling bone screws are therefore preferably used. Such self-drilling bone screws have the advantage that they can be screwed relatively easily into a bone or a bone fragment by the surgeon, without preliminary treatment of the bone or the bone fragment being required, for example by the insertion of a bore or the like.
To be easily screwed into the bone or the bone fragment, self-drilling bone screws generally have a screw tip with a smallest possible tip angle. In particular with longer screws the problem frequently occurs, however, that the screw tip bends or even breaks when screwed into the bone or the bone fragment.
A self-drilling bone screw is known from U.S. Pat. No. 5,925,048 which comprises a head and a shank provided with a thread. The screw has a total length of 4 to 14 mm and a tip angle of 45 to 50°.
The object of the invention is to provide a self-drilling bone screw which can be easily and rapidly screwed into a bone or a bone fragment and in which, at the same time, bending or even breaking of the screw tip can be reliably avoided when screwing in.